1. Field
This disclosure relates to multi-band and broadband microwave antennas.
2. Description of the Related Art
The microwave portion of the electromagnetic spectrum includes a plurality of defined frequency bands commonly used for radar and communications systems. For example, the Institute of Electrical and Electronic Engineers defines a series of “radar bands” including the C band from 4 to 8 GHz, the X band from 8 to 12 GHz, the Ku band from 12 to 18 GHZ, the K band from 18 to 27 GHz, and the Ka band from 27 to 40 GHz. Within the broadly defined radar bands, specific communications bands may be used for terrestrial and satellite communications. Each of the communications bands may correspond to an atmospheric frequency window, or wavelength range that is transmitted through the atmosphere with relatively low loss. In addition, both radar and communications systems commonly use orthogonally polarized signals within the same frequency band to transmit or receive different information. Thus, many applications require dual polarization broadband or multi-band antennas useable to transmit and/or receive microwave signals in more than one band.
Traditional microwave antennas may use different components to combine or separate signals having different polarization states and different frequencies. For example, the feed network of a traditional dual polarization multi-band antenna may include a diplexer, or frequency multiplexer, to mix or separate signals in two frequency bands, and two band-specific ortho-mode transducers to combine or separate orthogonally polarized signals in each frequency band. The resulting feed network may be costly, mechanically complex, and bulky.
Waveguides and waveguide horns are commonly used to convey and radiate microwave energy. In most applications, the operational bandwidth of a waveguide or waveguide horn is considered to be the range of electromagnetic waves that can propagate within the waveguide as a single fundamental mode or a pair of orthogonal fundamental modes. The addition of conductive ridges in the walls of a waveguide is known to increase the bandwidth of the waveguide.
Throughout this description, elements appearing in figures are assigned three-digit reference designators specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having the same reference designator.